Engineering Commons^™

Efficiency Performance Improvement Using Parallel Dc-Dc Converters With A Digital Controller, Daniel Forbes

Master's Theses

A system to improve efficiency performance of a DC-DC converter is simulated and built. The proposed system combines multiple DC-DC converters in parallel and implements a digital control scheme and load-share controller. A model of the system is developed in MATLAB Simulink and the model demonstrates the improved converter’s efficiency particularly at low load conditions. This simulation is then designed into a hardware system running three DC-DC converters in parallel, controlled by a microcontroller and a load-share controller. The hardware also confirms the simulation results, although some hardware refinements are evident as simulation results are superior. The system is designed …

Best Management Practices Effectiveness To Reduce Sediment Transport To Morro Bay, Michael J. Randall

Master's Theses

The Morro Bay Watershed, which is located inSan Luis Obispo County,California, covers more than 48,000 acres of land and discharges intoMorroBaythrough the Morro Bay National Estuary (MBNE). The Chorro Creek Subwatershed consists of approximately 30,000 acres of the overall watershed. The MBNE provides an ecosystem that supports a variety of wildlife from the common sea gull to the endangered sea otter. The estuary is also home to over 200 species of birds. The operational waterfront of theMorroBayHarborwas and continues to be a strong supporter to the local economy of the City of Morro Bay. Numerous studies were conducted since the …

Mechanical Properties Of Bone Due To Sost Expression: A 3-Point Bending Assessment Of Murine Femurs, Kainoa John Peterson

Master's Theses

Sclerostin, a protein coded for by the SOST gene, is an osteocyte-expressed negative regulator of bone formation. The absence of SOST in the genome may have an effect on bone formation both during skeletal maturation and full maturity. This study attempts to determine significant differences in the mechanical properties of bone that expresses SOST compared to bone that does not. One hundred femur samples from 6, 8, and 12 month old mice were obtained from Lawrence Livermore National Labs and loaded until failure using three-point bending. Results showed significant differences in treatment group effects for cross sectional area, yield force, …

Patient And Nurse Considerations In Home Health Routing With Remote Monitoring Devices, Jessica Spicer

Graduate Theses and Dissertations

We build on the current consistent vehicle routing problem literature by formulating a novel multi- objective mathematical model of the home health scheduling and routing problem that includes the option of assigning some patient visits to remote monitoring devices, with the objectives of mini- mizing total cost, achieving nurse consistency and creating balanced nurse workloads. A heuristic solution approach that approximates the efficient frontier of this multiobjective problem is pre- sented and validated, and the results of using this methodology to solve several realistic instances are included. We also analyze the assignment of patients to devices and present some managerial …

Flushing Of A Dense Fluid From An Isolated Urban Canyon, Zahra Baratian-Ghorghi

All Dissertations

The mechanics of shear-driven flushing of a dense fluid from a canyon is investigated through a series of laboratory experiments. Such a flow has many environmental applications including the removal of dense pollutants trapped in urban canyons and the purging of salt water from bed depressions at river mouths. While there is an extensive literature on flow in canyons and cavities for the neutrally buoyant case, the problem of flushing a dense fluid from canyon has received considerably less attention. To understand the dynamics of the mixing and to quantify the buoyant contaminant flushing rate, a broad range of experimental …

Glottal Excitation Extraction Of Voiced Speech - Jointly Parametric And Nonparametric Approaches, Yiqiao Chen

All Dissertations

The goal of this dissertation is to develop methods to recover glottal flow pulses, which contain biometrical information about the speaker. The excitation information estimated from an observed speech utterance is modeled as the source of an inverse problem.
Windowed linear prediction analysis and inverse filtering are first used to deconvolve the speech signal to obtain a rough estimate of glottal flow pulses. Linear prediction and its inverse filtering can largely eliminate the vocal-tract response which is usually modeled as infinite impulse response filter. Some remaining vocal-tract components that reside in the estimate after inverse filtering are next removed by …

Design Of Meta-Materials Outside The Homogenization Limit Using Multiscale Analysis And Topology Optimization, Christopher Czech

All Dissertations

The field of meta-materials engineering has largely expanded mechanical design possibilities over the last two decades; some notable design advances include the systematic engineering of negative Poisson's ratio materials and functionally graded materials, materials designed for optimal electronic and thermo-mechanical performances, and the design of materials under uncertainty. With these innovations, the systematic engineering of materials for design-specific uses is becoming more common in industrial and military uses. The motivation for this body of research is the design of the shear beam for a non-pneumatic wheel. Previously, a design optimization of a finite element model of the non-pneumatic wheel was …

Algebraic Approaches To Stochastic Optimization, Katherine Hastings

All Dissertations

The dissertation presents algebraic approaches to the shortest path and maximum flow problems in stochastic networks. The goal of the stochastic shortest path problem is to find the distribution of the shortest path length, while the goal of the stochastic maximum flow problem is to find the distribution of the maximum flow value. In stochastic networks it is common to model arc values (lengths, capacities) as random variables. In this dissertation, we model arc values with discrete non-negative random variables and shows how each arc value can be represented as a polynomial. We then define two algebraic operations and use …

Surface Damage In Retrieved Total Knee Replacement Femoral Components, Estefania Alvarez

All Dissertations

The metallic femoral components of total knee replacements are subject to in vivo surface damage and roughening that can severely limit the service lifetime of the bearing system. To date, there are no national standards by which to characterize the severity and damage modes of these critical bearing surfaces, and therefore it remains difficult to accurately assess how femoral damage influences total joint replacement bearing longevity. In vitro and in vivo studies have shown that severe surface damage of the femoral component can occur, however, there is still no defined test methodology that can identify or replicate the types of …

Compressive Strength Of Continuous Fiber Unidirectional Composites, Ronald Thompson

All Dissertations

Dow and Rosen's work in 1965 formed an intellectual framework for compressive strength of unidirectional composites. Compressive strength was explained in terms of micro-buckling, in which filaments are beams on an elastic foundation. They made simplifying assumptions, with a two dimensional idealization and linearized material properties. This study builds on their model, recognizing that the shear mode of instability drives unidirectional compressive strength. As a necessary corollary, the predictive methods developed in this study emphasize correct representation of composite shear stiffness. Non-linear effects related to matrix material properties, fiber misalignment, three dimensional representation, and thermal prestrains are taken into account. …

Synthesis Of Gallium Nitride By Laser-Assisted Metal Organic Vapor Phase Epitaxy, Matthew J. Mitchell

Department of Electrical and Computer Engineering: Dissertations, Theses, and Student Research

For the past two decades, gallium nitride (GaN) has become one of the most studied materials in the fields of optics and electronics due to its unique properties.Currently available methods for the synthesis of GaN require a high substrate temperature of 1100 ^oC, which can lead to several issues including a high defect concentration and increased probability of cracking and warping of films due to differences in thermal expansion coefficients between the substrate and film. The high growth temperature also prevents the integration of GaN devices with CMOS fabrication techniques, which has a post-process temperature limit of ~575 oC. …

Wireless Communications Under Qos Constraints: Energy Efficiency, Power And Rate Control, And Throughput, Deli Qiao

Department of Electrical and Computer Engineering: Dissertations, Theses, and Student Research

This dissertation deals with various issues in wireless communications under statistical quality of service (QoS) constraints. Effective capacity, which provides the maximum constant arrival rate that a wireless channel can sustain while satisfying statistical QoS constraints, is adopted as the performance metric. Energy efficiency of point-to-point links is first studied by characterizing the spectral efficiency-bit energy tradeoff in the low-power and wideband regimes. Different transmission strategies (with variable or fixed rate) and power policies are studied. Then, the effective capacity region for fading multiple-access channels (MAC) is investigated for different transmission strategies: Superposition coding with successive decoding and time division …

Multi-Circle Detections For An Automatic Medical Diagnosis System, Dingran Lu

Master's Theses

Real-time multi-circle detection has been a challenging problem in the field of biomedical image processing, due to the variable sizes and non-ideal shapes of cells in microscopic images. In this study, two new multi-circle detection algorithms are developed to facilitate an automatic bladder cancer diagnosis system: one is a modified circular Hough Transform algorithm integrated with edge gradient information; and the other one is a stochastic search approach based on real valued artificial immune systems. Computer simulation results show both algorithms outperform traditional methods such as the Hough Transform and the geometric feature based method, in terms of both precision …

Bubble Coalescence And Breakup Modeling For Computing Mass Transfer Coefficient, Ryan A. Mawson

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

Modeling fluid behavior with computer numerical models can be very difficult due to the physical phenomenon which can be present in complex fluid systems. One difficult situation to model is when there is more than one type of fluid in a system. Some of these systems include fluids which do not mix, such as is the case when a liquid and a gas are present. In this situation, the gas phase will form bubbles which are dispersed throughout the liquid phase. Modeling the breakup and coalescence of these bubbles is critical to correctly model this type of situation.

There exist …

A Refreshable And Portable E-Braille System For The Blind And Visually Impaired, Mohammad Yousef Saadeh

UNLV Theses, Dissertations, Professional Papers, and Capstones

The objective of this research is to design an affordable Braille tactile display that is wearable, refreshable, and portable. The device is intended to be used as an output device that can playback stored media. It can be also incorporated with current Braille reading technologies. The device will control both the electrical and mechanical stimulations to optimize the sensation and ensure extended use of the device. This work is concerned mainly with the mechanical aspects of the design.

This research proposed the development of a finger-wearable, scanning-style electric stimulation based (electrotactile) Braille display with sensing and adaptive rendering/actuation functions for …

Transversely Post-Tensioned Box-Beam System For Precast Parking Structures, Jenna Hansen

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Parking structures are essential to any growing commercial district, yet little thought is given to their longevity and appearance. This is particularly the case with precast parking structures. Typical issues include poor joint performance and the impact of stemmed members on interior building aesthetics. Research provided in this report proposes an alternate design that improves long term joint performance and optimizes the perspective spacing between deck members. These benefits (along with the others) are incorporated to reflect the benefits of parking structures designed using cast-in-place concrete and structural steel with concrete decking. Other benefits include: flexible column spacing, reduced / …

Safety Investigation And Guidance For Retrofitting Existing Approach Guardrail Transitions, Eric R. Jowza

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Throughout the United States, various approach guardrail transition systems are routinely implemented by State Highway Departments to connect standard strong-post, W-beam guardrail systems to the blunt end of concrete bridge rails and roadside median barriers. When installed correctly, approach guardrail transitions shield the hazardous exposed ends of rigid parapets as well as significantly reduce the propensity for wheel snag and vehicle pocketing throughout the transition region. Unfortunately, approach guardrail transitions that are installed in the field may not always resemble that of the as-tested configuration, thus reducing the desired lateral stiffness and strength of the transition system. A recent survey …

An Evaluation Of Non-Intrusive Traffic Detectors At The Ntc/Ndor Detector Test Bed, Benjamin W. Grone

Department of Civil and Environmental Engineering: Dissertations, Theses, and Student Research

Throughout the field of transportation engineering, decision makers require quality information. The information used in transportation operations, planning, and design is based, in part, on data from traffic detectors. The need for quality data has spurred innovations in data collection including the introduction of modern, commercially available, non-intrusive traffic detectors. As these new technologies become available, a need exists to understand their capabilities and limitations—especially limitations that are unique to a specific region.

This thesis examined the accuracy of four non-intrusive traffic detector technologies considered for potential data collection applications on Nebraska’s highways. The technologies evaluated included the Solo Pro …

Real-Time Characterization Of Ultra-Thin Organic Layers Via Simultaneous Spectroscopic Ellipsometry And Piezoelectric Nanogravimetry, Keith B. Rodenhausen Jr.

Department of Chemical and Biomolecular Engineering: Dissertations, Theses, and Student Research

Analysis techniques are needed to determine the quantity and structure of materials composing an organic layer that is below an optical ultra-thin film limit and in a liquid environment. Neither optical nor acoustical techniques can independently distinguish between thickness and porosity of ultra-thin films due to parameter correlation. A combined optical and acoustical approach yields sufficient information to determine both thickness and porosity. The author describes application of the combinatorial approach to measure single or multiple organic layers when the total layer thickness is small compared to the wavelength of the probing light. The instrumental setup allows for simultaneous in-situ …

System Selection Based On Controlled Risk, Lina Wang

Department of Industrial and Management Systems Engineering: Dissertations, Theses, and Student Research

The studies of using computer simulation to address stochastic systems selection problem prevail currently. Ranking and selection procedures are statistical procedures that can be used in the field of computer simulation to select the best system or the subset that includes the best system based on a performance metric of the interest with a guaranteed correct selection. The best system is defined in the majority of selection problems as a system with the largest (or smallest) mean value. However, mean is only a measure of the average behavior. Risk, which influences the stability of a system to a large extend, …

A Conductivity Testing System Coupled With A Tensile Testing Machine To Measure The Surface Properties Of Polymer Specimens, Nguyen T. Nguyen

Department of Mechanical and Materials Engineering: Dissertations, Theses, and Student Research

Polymers play an essential role in our everyday life due to their employment in a widespread range of applications. Polymers are used in industries such as space, biomedical, electronics, etc. in which their electrical and mechanical properties are major aspects which need to be investigated prior to implementation. When subjected to mechanical stimulations, polymers may exhibit changes in electrical conductivity which can vary locally within the specimens, especially in those of conducting polymers. In mechanical investigations a tensile testing machine is used to understand polymers’ strength, elasticity or other mechanical properties. In electrical analysis, using a four-point probe to examine …

Evaluation Of A Bisphosphonate Enriched Ultra-High Molecular Weight Polyethylene For Enhanced Total Joint Replacement Bearing Surface Functionality, Cassandra Wright-Walker

All Dissertations

Each year in the United States there is an increasing trend of patients receiving total joint replacement (TJR) procedures. Approximately a half million total knee replacements (TKRs) are performed annually in the United States with increasing prevalence attributed to baby-boomers, obesity, older, and younger patients. This trend is also seen for total hip replacements (THRs) as well. The use of ultra high molecular weight polyethylene (UHMWPE) inserts in TJRs results in wear particle-induced osteolysis, which is the predominant cause for prosthesis failure and revision surgery. Sub-micron size particle generation is inevitable despite the numerous efforts in improving this bearing material. …

Computational Representation And Reasoning Support For Requirements Change Management In Complex System Design, Beshoy Morkos

All Dissertations

Requirements play a critical role within any design process and the activity of identifying and maintaining a system's requirements is essential to. However, design is a complex and iterative process, where requirements are continuously evolving and are volatile. This change, if not managed, may result in undesired uncertainty within the design process leading to monetary losses and time delays, as the changing of requirements has been recognized as a major cause of project failure. In order to mitigate issues that arise due to requirement change propagation, this research presents a computational reasoning tool to help designers and engineers predict change …

Assessing Ongoing Sources And Fate Of Dissolved Polychlorinated Biphenyls (Pcbs) In A Stream, Viet Dang

All Dissertations

Polychlorinated biphenyls (pcbs) contamination remains a concern due to their persistence and the risk to human health associated with them. Once released into the environment, these substances are mainly associated with sediment particles and sediment organic carbon matter. They bioaccumulate in organisms via contaminated food and only a small faction is desorbed from sediment into the water column. Given the discontinuity of active discharge, pcbs are currently entering the water via groundwater inputs, soil erosion, and/or ongoing leakage from the point source. It is the dissolved form that 1) can be either absorbed by biofilm attached to stream leaves, which …

Expert System Based Approach For Material Selection Of Automobile Body-In-White Structural Panels Using Numerical Ranking And Sustainability Indices, Ahmad Mayyas

All Dissertations

The goal of this work is to establish a set of quantifiable measures for design for sustainability (DFS) that can be applied to automotive applications in terms of environmental, social, economic and technical aspects. In this study, a comprehensive analysis was made in order to develop a methodology that can evaluate different body-in-white designs in terms of major sustainability aspects. Besides the complete life cycle analysis, environmental impacts and cost factors will be analyzed over vehicle's entire life-cycle (fuel extraction and refining, Pre-manufacturing, Manufacturing, Use, and
Post-use stages). The considered material options include: conventional steel, high strength steel, aluminum, magnesium, …

A Study Of Environment Noise In Ultra-Wideband Indoor Position Tracking, William Suski

All Dissertations

This work is motivated by the problem of improving the accuracy of indoor ultra-wideband (UWB) position tracking through the study of the environment noise that affects such a system. Current systems can provide accuracy in the range of 30-100 cm in a small building, suitable for applications that require rough room-level precision such as asset tracking and surveillance. Our long-term goal is to improve the accuracy to 1 cm or better, expanding potential applications to telepresence, augmented reality, training and entertainment.
This work investigates the possibility of systematically observing the measurement noise of an UWB position tracking system and building …

Clustering And Classification Of Multivariate Stochastic Time Series In The Time And Frequency Domains, Ryan Schkoda

All Dissertations

The dissertation primarily investigates the characterization and discrimination of stochastic time series with an application to pattern recognition and fault detection. These techniques supplement traditional methodologies that make overly restrictive assumptions about the nature of a signal by accommodating stochastic behavior. The assumption that the signal under investigation is either deterministic or a deterministic signal polluted with white noise excludes an entire class of signals -- stochastic time series. The research is concerned with this class of signals almost exclusively. The investigation considers signals in both the time and the frequency domains and makes use of both model-based and model-free …

First Generation College Students In Engineering: A Grounded Theory Study Of Family Influence On Academic Decision Making, Denise Simmons

All Dissertations

This work develops a constructivist grounded theory describing the influence of family and those that serve a role similar to family on the academic decision making of undergraduate first generation in college (FGC) students majoring in engineering. FGC students, in this study, are students with neither parent having attained a bachelor's degree.
FGC students are an untapped talent pool with the potential to diversify and increase the number of engineers, which are both urgent national priorities. Much is known about FGC students with respect to their academic preparation, transition to postsecondary education, and progress toward degree attainment. However, the literature …

Quantitative, Spatial Imaging Based Measurements To Assess Cellular Health And Oxygenation In A Tissue Engineered Test System, Erik Bland

All Dissertations

Three-dimensional in vitro tissue test systems are employed to examine cell behavior, test responses to drugs and vaccines, and answer basic biological questions. These systems are more physiologically relevant than two-dimensional cell cultures, and are more relevant, easier and less expensive to maintain than animal models. However, methods used to measure cell behavior and viability have been developed specifically for two-dimensional cell cultures or animal models, and are often not optimally translated to three-dimensional in vitro test systems. The purpose of this work was to aid in the development of three-dimensional, spatially controlled in vitro test systems, and to develop …

Grain Boundaries Structures And Wetting In Doped Silicon, Nickel And Copper, Kaveh Meshinchi Asl

All Dissertations

This thesis reports a series of fundamental investigations of grain boundary wetting, adsorption and structural (phases) transitions in doped Ni, Cu and Si with technological relevance to liquid metal embrittlement, liquid metal corrosion and device applications. First, intrinsically ductile metals are prone to catastrophic failure when exposed to certain liquid metals, but the atomic level mechanism for this effect is not fully understood. A nickel sample infused with bismuth atoms was characterized and a bilayer interfacial phase that is the underlying cause of embrittlement was observed. In a second related study, we showed that addition of minor impurities can significantly …